Mixed-State Ionic Beams: An Effective Tool for Collision Dynamics Investigations

The use of mixed-state ionic beams in collision dynamics investigations is examined. Using high resolution Auger projectile spectroscopy involving He-like ( 1 s 2 1 S , 1 s 2 s 3 , 1 S ) mixed-state beams, the spectrum contributions of the 1 s 2 s 3 S metastable beam component is effectively separated and clearly identified. This is performed with a technique that exploits two independent spectrum measurements under the same collision conditions, but with ions having quite different metastable fractions, judiciously selected by varying the ion beam charge-stripping conditions. Details of the technique are presented together with characteristic examples. In collisions of 4 MeV B 3 + with H 2 targets, the Auger electron spectrum of the separated 1 s 2 s 3 S boron beam component allows for a detailed analysis of the formation of the 1 s 2 s ( 3 S ) n l 2 L states by direct n l transfer. In addition, the production of hollow 2 s 2 p 1 , 3 P doubly- and 2 s 2 p 2 2 D triply-excited states, by direct excitation and transfer-excitation processes, respectively, can also be independently studied. In similar mixed-state beam collisions of 15 MeV C 4 + with H 2 , He, Ne and Ar targets, the contributions of the 1 s 2 , 1 s 2 s 3 , 1 S beam components to the formation of the 2 s 2 p 3 , 1 P states by double-excitation, 1 s → 2 p excitation and transfer-loss processes can be clearly identified, facilitating comparisons with theoretical calculations.